Calcining of gypsum comprises converting calcium sulfate dihydrate by heating into calcium sulfate hemihydrate, better known as stucco. Prior calcining apparatus and methods have taken various forms. Traditionally, the calcining of gypsum has occurred in a large kettle, having a thickened dome-shaped bottom, against which a gas-fired flame is directed, with the kettle and burner flame being enclosed in a suitable refractory structure. There is usually an associated hot pit into which the calcined material is fed. The kettle must withstand temperatures in the 2,000°–2,400° F. range, hence requiring expensive fire box steel plate on its domed bottom, which was typically 1¾ inches thick. U.S. Pat. No. 3,236,509 typifies this type construction. This approach had numerous disadvantages, such as the extreme waste of hot burner gases, and the associated refractory brick enclosure which, when repairs or kettle shut-down were needed, first required a lengthy cool-down period.
After the gypsum has been calcined, further processing is sometimes required. The calcined gypsum, or stucco, can be placed in a fluid bed stucco cooling apparatus wherein water is sprayed into the apparatus to cool the stucco to a predetermined temperature. In addition, other types of stucco processing apparatus are known such as a cooling coil fluid bed stucco treaters where the stucco is cooled with a cooling coil that is positioned within the apparatus to control the temperature of the stucco. Other processing apparatus such as post-stucco treatment retention devices can be used in the manufacture of gypsum-based products.